What is your pressure and GPM.....i would assume this screaching sound is coming from your valves......there are different reasons why this may happen...with excessive pressure is in the system, the valves will slam (pretty lousdly open and especially closed) (known as water hammer) i had once gone on a service call to a homeowner who attempted to install the system himself,,but had a few problems he was too lazy to fix..he tapped off the outdoor faucet rigtht off the spigot, using a hose to pipe converter, and a regular hose quick connector...when the system turns on, the quick connector screethced until all sprinklers were fully in action. Of course, the proper way to tap is at the main,.,,,so that was something else.....where did you tap?? I am assuming that the valves are the screetching items rite? Let me know!
Thanks
Ray
Rays Above and Beyond Automatic Lawn Sprinklers